Sunday, 1 June 2014

calculus - prove that a function is continuous if the denominator is a continuous function



Given that f(x) is a continuous function and its value is positive at point x0 I need to prove that:
f(x)+1f(x)
is continuous at x0. I think this is really easy but not 100% sure. My thinking is:
1) because f(x) is continuous at x0 then limxx0f(x) exists (definition of a continuous function at a given point).



2) Let's see if limxx0f(x)+1f(x) exists: limxx0f(x)+1f(x)=limxx0(f(x))2+1f(x), provided that f(x)0 which is given hence the limit exists.




3) According to arithmetic of continuous functions (f(x))2+1f(x) is valid because the denominator will never be 0. Thus the (f(x))2+1f(x) is continuous at x0.


Answer



we introduce g, such as g(x)=f(x)+1f(x), which is the sum of two functions .



We know that f is continuous at x0 and non-null ( I guess), therefore, the inverse of this function is also continuous at that point.



The sum of two continuous functions at one point, is continuous, therefore g is continuous at x0


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